highlights – understanding of biodegradation...• a handful of respondents also want to know if...

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© Synovate 2010 1

Highlights – Understanding of Biodegradation

•  Over 60% of respondents claimed they understand the meaning of “biodegradable” quite well*. -  Of all the venues in which respondents were asked where products

labelled biodegradable would decompose, “landfills” received the highest score (72%) followed by “open environment” (51%) and “commercial composting” (51%)

-  4 out of 5 (80%) respondents believe biodegradation in landfills is dissimilar to biodegradation in a composting environment

-  More than half of the respondents (55%) were unaware that landfills currently capture gases generated as a result of biodegradation and convert them to energy

*When asked to rate their understanding of the word biodegradable on a 5-point scale where 5 = I know it very well and can explain it to someone, 64% of respondents rated their understanding as being a 4 or 5.

© Synovate 2010 2

“What are the differences between biodegradation in landfills vs. biodegradation in composting environments?”

•  Many respondents attributed the differences to composition (27%), degradation process (26%), and/or duration of degradation (23%). -  Respondents defined composition as what exactly goes into each

environment and their levels of aeration -  For the degradation process, respondents cited the end product of

landfills as garbage and as soil for compost piles. Also they compared the ability of one over another to biodegrade matter, and referenced a presence of additives

-  Of those who mentioned factors related to the duration of degradation, the majority said landfills take longer to biodegrade

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© Synovate 2010 3

Highlights – Biodegradation of Plastics

•  A good majority of respondents (72%) believe traditional plastics will not biodegrade on their own. -  Those who think plastics do biodegrade on their own think it mainly

happens in landfills or commercial composting sites

•  A large number of respondents (84%) believe biodegradable plastic products will be beneficial to landfills. -  74% believe biodegradable plastics will reduce the burden on landfills

•  7 out of 10 (70%) respondents were okay with a 5 year or less window for duration of the biodegradation of biodegradable plastic packages. -  25% of respondents believe plastics should biodegrade in less than

one year

© Synovate 2010 4

Highlights – Package Labeling

•  An overwhelming number of respondents (93%) think it is okay to label a package “biodegradable” if it decomposes in a landfill.

•  A majority of respondents (63%) think it is not okay to label a package “biodegradable” if it only decomposes in a commercial composting facility and not in their back yards.

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© Synovate 2010 5

“What information would you like to see on a package labeled biodegradable?” •  Most respondents would like to know how long it takes a

package to biodegrade (39%), where it biodegrades (27%), the conditions under which it biodegrades (18%), and/or what to do with the package when they’re done with it (10%).

•  A handful of respondents also want to know if the product was safe to use and not harmful once disposed of. -  Examples: “Will biodegrade in less than 5 years in any

environment. But, none of the chemicals used to make this new biodegradable product harmful to our health as we drink or eat from it.”

-  “Safety of the by-products and the time to completely biodegrade.”

© Synovate 2010 6

Highlight – Attitude towards “green”

•  Less than 2 out of 5 (38%) respondents claimed they often or always check for green aspects on a product label.

•  Of the 6 attributes that contribute toward lowering a product’s burden on the environment, respondents believe “biodegradable” and “recyclable” are the most important.

•  Over 6 out of 10 (62%) respondents stated they are willing to pay a higher price for products that are less burdensome on the environment.

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Renewable Energy 32 (2007) 1243–1257

Methane generation in landfills

Nickolas J. Themelis!, Priscilla A. Ulloa

Earth Engineering Center and Department of Earth and Environmental Engineering, Columbia University,New York, NY 10027, USA

Received 1 July 2005; accepted 15 April 2006Available online 2 August 2006

Abstract

Methane gas is a by-product of landfilling municipal solid wastes (MSW). Most of the globalMSW is dumped in non-regulated landfills and the generated methane is emitted to the atmosphere.Some of the modern regulated landfills attempt to capture and utilize landfill biogas, a renewableenergy source, to generate electricity or heat. As of 2001, there were about one thousand landfillscollecting landfill biogas worldwide. The landfills that capture biogas in the US collect about 2.6million tonnes of methane annually, 70% of which is used to generate heat and/or electricity. Thelandfill gas situation in the US was used to estimate the potential for additional collection andutilization of landfill gas in the US and worldwide. Theoretical and experimental studies indicate thatcomplete anaerobic biodegradation of MSW generates about 200 Nm3 of methane per dry tonne ofcontained biomass. However, the reported rate of generation of methane in industrial anaerobicdigestion reactors ranges from 40 to 80Nm3 per tonne of organic wastes. Several US landfills reportcapturing as much as 100 Nm3 of methane per ton of MSW landfilled in a given year. These findingsled to a conservative estimate of methane generation of about 50Nm3 of methane per ton of MSWlandfilled. Therefore, for the estimated global landfilling of 1.5 billion tones annually, thecorresponding rate of methane generation at landfills is 75 billion Nm3. Less than 10% of thispotential is captured and utilized at this time.r 2006 Elsevier Ltd. All rights reserved.

Keywords: Landfill gas; Renewable energy; Municipal solid waste; Biogas; Methane emissions

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www.elsevier.com/locate/renene

0960-1481/$ - see front matter r 2006 Elsevier Ltd. All rights reserved.doi:10.1016/j.renene.2006.04.020

!Corresponding author. Tel.: 1 212 854 2138; fax: 1 212 854 5213.E-mail addresses: [email protected] (N.J. Themelis), [email protected] (P.A. Ulloa).

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1. Introduction

Part of the methane generated in landfills can be captured and used as a renewableenergy source. In contrast, when methane is allowed to escape to the atmosphere, it has aglobal warming potential that IPPC [1] estimates to be 23 times greater than that of thesame volume of carbon dioxide. In his 2003 review of energy recovery from landfill gas,Willumsen [2,3] reported that as of 2001 there were about 955 landfills that recoveredbiogas or landfill gas. The largest number existed in the US followed by Germany andUnited Kingdom (Table 1). The capacity of most landfill gas-fuelled generators rangedfrom 0.3 to 4 MW. While the largest biogas plant in the world is at the Puente Hills landfill,close to Los Angeles California; the biogas is combusted in a steam boiler that powers a50-MW turbine generator [4].Willumsen also provided detailed information on 21 landfills in Denmark that in total

captured about 5800Nm3 of biogas/h, equivalent to 27.4 MW of contained thermalenergy. For comparison purposes, Denmark captures 20,000 tonnes of methane/y, whilethe US captures 2,600,000 tonnes.

1.1. US landfilling

In 2002, the Earth Engineering Center of Columbia University collaborated withBioCycle journal in a US-wide survey of the amount of municipal solid wastes (MSW)generated in the US and how they were disposed [5,6]. The results are summarized andcompared with USEPA values [7] in Table 2 below.

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Table 1Energy recovering landfills [3]

Country Number of plants

United States 325Germany 150United Kingdom 135Sweden 70Holland 60Italy 40Canada 25Australia 25Denmark 21Norway 20Austria 15France 10Spain 10Switzerland 10Finland 10Poland 10Brazil 6Czech Republic 5Hungary 5China 3

Total 955

N.J. Themelis, P.A. Ulloa / Renewable Energy 32 (2007) 1243–12571244

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1.2. Global landfilling

The per capita generation of MSW in the US of 1.19 tonnes is twice as large as the totalgeneration (i.e. before any recycling) of MSW per capita in the affluent nations of E.U. andJapan. This is expected because the consumption of materials and fossil fuels in the US,with 5% of the world population, amounts to 20–25% of the total global consumption.

To arrive at a rough estimate of global landfilling, we started with the known rate oflandfilling in the US (220 million tonnes). The European Union (EU), and the rest of the‘‘golden billion’’ who enjoy a high standard of living generate an estimated 420 milliontonnes of MSW of which at least 210 million tonnes (50%) are landfilled. Wastemanagement studies in developing nations, including some in Africa, have shown that theMSW generation is always higher than 0.2 tonnes per capita, most of which is food andyard wastes and is landfilled. This results in the estimate of 1080 million tonnes for the 5.4billion people in the developing world. Adding up these estimates indicates that the globalMSW landfilled is somewhere close to 1.5 billion tonnes of MSW.

2. Landfill dumps and regulated landfills

Broadly, landfills can be classified into two types. The most common ones, still usedthroughout the developing world, consist of dumps where the MSW is deposited until itreaches a height that for esthetic or technical reasons is considered to be the desirablemaximum. After closing a landfill, some soil is deposited on top.

In October 1988, the US Environmental Protection Agency (USEPA) reported to theCongress that municipal solid wastes were landfilled in nearly 6,500 landfills. Althoughthese landfills used a wide variety of environmental controls, they posed significant threatsto groundwater and surface water resources, as well as health effects due a threat to air andwater. To address these concerns, and standardize the technical requirements for MSWlandfills, USEPA promulgated revised minimum federal criteria for MSWLFs on October9, 1991 [8]. As a result of these more stringent regulations, many of the smaller landfillswere closed and at the present time there are only 1767 landfills EPA [7]. Large landfilloperations have taken advantage of economies of scale by serving large geographic areasand accepting other types of wastes, such as commercial solid waste, non-hazardoussludge, and industrial non-hazardous solid wastes. In 2000, an estimated 75% of the USmunicipal solid waste was deposited in 500 large landfills [9].

Regulated landfills are provided with impermeable liners and caps, and leachatecollection and treatment systems. Also, a system of gas wells and pipes collects as much as

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Table 2Generation and fate of MSW in the US [5–7]

14th SOG survey [3,4] USEPA 2001 survey [5]

Million tonnes/yr (%) Million tonnes/yr (%)

Amount generated 336 100 211 100Amount recycled and composted 90 26.7 65 30.8Amount to waste-to-energy 26 7.7 27 12.8Amount landfilled 220 65.6 119 56.4

N.J. Themelis, P.A. Ulloa / Renewable Energy 32 (2007) 1243–1257 1245

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possible of the landfill gas (LFG) and conveys it to a boiler or turbine where it iscombusted to generate heat or electricity, or is simply flared. When the landfilled areareaches its maximum height, it is covered with an impervious layer so as to minimize entryof rainwater and, thus, continuation of the bioreactions within the landfill. Also, USlandfill operators are required to continue collecting and treating gas and liquid effluentsfor a period of 30 years after closure of the landfill.A variation of the regulated landfill that is being tested in the US with some measure of

success is the ‘‘bioreactor’’ landfill. In this case, instead of preventing water from entering,the aqueous effluent is recirculated and distributed throughout the landfill. The objective isto accelerate the rate of biochemical degradation of the MSW, thus increasing thegeneration of methane gas and, because of increased settling, the storage capacity of thelandfill.The European requirements for non-hazardous, Class II landfills are similar to the US

and are based on the standards established by French regulations in January 1996.However, the EU Landfill Directive of 1999 [10] requires that in the near future, landfillingbe limited to inert materials that are not biodegradable or combustible. Nevertheless, itmay take decades before this directive is applied in the new nations joining the EU, so thegeneration of landfill gas will continue for the foreseeable future. In contrast to the EU andJapan, landfilling remains the preferred means of MSW disposal in the US.

3. Composition of biomass in MSW

Table 3 is based on the characterization of US MSW [7]. Biomass materials, i.e. paper,food and yard wastes, wood, leather, cotton and wool, constitute 69.5% of the MSW andpetrochemicals another 15%. The rest are inorganic materials such as metals, glass,gypsum, and other minerals.By using the ultimate (atomic) analysis of various types [11] of wastes and the atomic

weights of the respective elements, it was possible [12] to derive the composite molecularformulae corresponding to mixed food wastes and paper:Mixed food and green wastes: C6H9.6O3.5N0.28 S0.2.Mixed paper: C6H9.6O4.6N0.036 S0.01.It can be seen that sulfur and nitrogen are relatively minor components and occur

principally in mixed and green food wastes. Also, if one excludes nitrogen and sulfur, themolecular structure of mixed paper is very close to cellulose, (C6H10O5)x. If one excludes

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Table 3Characterization of US MSW by USEPA [7]

Biomass components (%) Petrochemical components (%)

Paper/board 36.2 Plastics 11.3Wood 5.8 Rubber, nylon, etc.a 3.7Yard trimmings 12.1Food scraps 11.7Cotton, wool, leathera 3.7

Total biomass 69.5% Total man-made 15.0%

aRubber, leather and textiles category of USEPA was assumed to be divided equally between natural and man-made products.


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the minor elements, the average molecular structure of organic compounds in MSW can beapproximated by the molecular composition C6H10O4 [12]. It is interesting to note that thiscomposition corresponds to the structural formula of at least ten organic compounds, such asethyl butanedioic acid, succinic acid, adipic acid, ethylene glycol diacetate, and others. Thethermodynamic heat of formation of most of these compounds is about !960MJ per kmol.

Landfill gas is a product of biodegradation of refuse in landfills, and it containsprimarily methane (CH4) and carbon dioxide (CO2), with trace amounts of non-methaneorganic compounds (NMOC) that include air pollutants and volatile organic compounds[13]. Table 4 shows the main compounds and their proportion of LFG.

3.1. Anaerobic biodegradation of MSW in landfills

Shortly after MSW is landfilled, the organic components start to undergo biochemicalreactions. In the presence of atmospheric air, that is near the surface of the landfill, thenatural organic compounds are oxidized aerobically, a reaction that is similar tocombustion because the products are carbon dioxide and water vapor. However, theprincipal bioreaction in landfills is anaerobic digestion that takes place in three stages. Inthe first, fermentative bacteria hydrolyze the complex organic matter into solublemolecules. In the second, these molecules are converted by acid forming bacteria to simpleorganic acids, carbon dioxide and hydrogen; the principal acids produced are acetic acid,propionic acid, butyric acid and ethanol. Finally, in the third stage, methane is formed bymethanogenic bacteria, either by breaking down the acids to methane and carbon dioxide,or by reducing carbon dioxide with hydrogen. Two of the representative reactions areshown below.

Acetogenesis

C6H12O6 ! 2C2H5OH" 2CO2: (1)

Methanogenesis

CH3COOH ! CH4 " CO (2)

CO2 " 4H2 ! CH4 " 2H2O: (3)

The maximum amount of natural gas that may be generated during anaerobicdecomposition can be determined from the approximate, simplified molecular formula thatwas, presented above:

C6H10O4 " 1:5H2O # 3:25CH4 " 2:75CO2: (4)

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Table 4Composition of landfill gas [13]

Compound Average concentration (%)

Methane (CH4) 50Carbon dioxide (CO2) 45Nitrogen (N2) 5Hydrogen sulphide (H2S) o1Non-methane organic compounds (NMOC) 2700ppmv


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This reaction releases a very small amount of heat and the product gas containsabout 54% methane and 46% carbon dioxide. The biogas, or landfill gas, also containswater vapor near the saturation point corresponding to the cell temperature, plussmall amounts of ammonia, hydrogen sulfide and other minor constituents. Therefore, inorder for anaerobic reaction to continue, it is necessary to supply the principal reagent,water.The ratio of the molecular weights of the composite organic compound (MW ! 146)

and water (MW ! 18) in Eq. (4) indicates that each kilogram of water can reactbiochemically with 5.4 kg of organics. Since on the average, MSW contains at least 20%moisture, there is just about sufficient moisture to react the contained biomass. However,the anaerobic bacteria thrive at water concentrations above 40%, so continuous additionof water is required.

3.2. Generation of methane per tonne of MSW

The typical MSW of Table 3 contains 69.5% of biomass materials. This includes thecontained moisture and inorganic dirt particles. Assuming that the dry organics amount to60% of the biomass results in the estimate of 417 kg (2.86 kmol) of C6H10O4 /tonne of totalMSW. A simple material balance based on Eq. (4) shows that complete reaction of onetonne of MSW would generate 208 standard cubic meters of methane biogas or 0.149tonnes of methane (1 kmol of CH4 is equal to 22.4Nm3).We shall now compare the above theoretical numbers with reported data of anaerobic

digestion in the literature. The rate of biodegradation of MSW in landfills was studied byBarlaz et al. [14] in small pilot plant columns that provided ideal temperature andconcentration conditions for bioreaction. As shown in Fig. 1, the reaction peakedat less than one hundred days and was nearly complete after about 320 days. Barlaz [15]estimated that the total amount of gas generated during this period was 213Nm3

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1.40

1.20

1.00

0.80

0.60

0.40

0.20

0.000 100 200 300 400

Day

mL

CH

4/da

y-da

y gm

Methane Rate

M1

M2

Fig. 1. Generation of methane in experimental apparatus simulating landfill bioreactions (M1 and M2 denote twodifferent tests; [14]).


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methane /dry tonne of biomass reacted (i.e. 0.153 tonnes methane /tonne of biomass). Thisnumber is in good agreement with the theoretical calculation presented above.

An analysis of several anaerobic digestion operations by Verma [16] showed that thereported rate of generation of biogas ranged from 100 to 200Nm3 of biogas (54–108Nm3

CH4) per tonne of wastes digested (estimated 60% biomass content). These numberscorrespond to generation rates from 73 to 135Nm3 methane per tonne of dry biomass.Therefore, during the two weeks or so of digestion in the anaerobic digestion reactor, thedegree of bioreaction ranges from 35% to 65% of that projected by Eq. (4).

In an earlier publication, Barlaz et al. [17] reported that methane generation rates at alandfill receiving 286,000 tonnes /y ranged from 0 to 90Nm3 /min. Assuming the mid-rangerate of generation of 45Nm3 per minute and that most of the gas is generated during thefirst year after the MSW is landfilled, indicates that about 83Nm3 or 0.12 tonnes ofmethane were generated /tonne of MSW.

It is interesting to note that the maximum capacity of landfilled MSW to producemethane was reported by Franklin [18] to be 62 standard m3 of methane per tonne ofMSW.

4. Estimates of global generation of methane from landfilling

USEPA estimated that the total anthropogenic emissions of methane were 282.6 milliontonnes in 2000 [19], of which 13% or 36.7 million tonnes were due to landfill emissions(Fig. 2). We will now attempt to assess the accuracy of this number.

As shown earlier, the global MSW landfilled was estimated at about 1.5 billion tonnes ofMSW. If it is assumed, on the basis of the data presented above, that on the average themethane generation is at least 50Nm3 of methane per tonne of MSW (i.e., at the low levelof reported anaerobic digestion rates), the global generation of methane from landfilledMSW is in the order of 75 billion standard cubic meters or 54 million tonnes of methane.

Stern and Kaufman [20] extrapolated the 1985 estimate of Subak et al. [21] of 36 milliontonnes of CH4 to earlier years, by assuming that MSW generation and landfilling were

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Manure4%

Rice11%

Natural gas15%

Coal8%

Oil1%

Solid waste13%

Waste water10%

Fuel stat, &mobile

1%

Biofuelcombustion

4%

Biomassburning

5%

Entericfermentation

28%

Global Anthropogenic CH4 Budget bySource in 2000

Fig. 2. Global anthropogenic methane [19].


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proportional to economic growth. On the basis of this assumption, and considering thatthe global economic growth from 1985 to 2000 was 58% [22], the 36 million tonnes ofmethane in 1985 extrapolate to 57 million tonnes in 2000. This number is in fairly goodagreement with the 54 million tonnes estimated by the present authors and is substantiallyhigher than the 36.7 million tonnes estimated by USEPA.

5. Capture of landfill gas

As mentioned earlier, modern landfills try to collect the biogas produced by anaerobicdigestion. However, the number of gas wells provided is limited (US average: about 1 well /4000m2 of landfill [18]), so that only part of the biogas is actually captured.Table 5 presents reported captured and estimated loss of methane for 25 landfills in

California. The landfilled MSW is reported by California Integrated Waste ManagementBoard [23] and the captured biogas was reported by Berenyi [24] and converted to methaneby multiplying by 54%. On the average, the captured methane amounted to 43Nm3 pertonne of MSW and the estimated methane loss to 82Nm3 per tonne of MSW.

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Table 5Landfill methane in California [23,24]

Landfill name MSW(Tonnes/yr)

Captured CH4

(Nm3/yr)Captured CH4

(Nm3/t MSW)Assumedgeneration(Nm3/t MSW)

Estimated lossCH4 (Nm3/t MSW)

Altamont 1,157,312 24,001,656 21 122 101Scholl Canyon 412,429 50,237,893 122 122Azusa 157,445 17,056,769 108 122 14Puente Hills #6 3,377,867 200,549,669 59 122 63Bradley Avenue West 418,341 40,190,314 96 122 26Crazy Horse 151,258 4,822,838 32 122 90Monterey Peninsula 197,797 3,351,872 17 122 105Prima Deshecha 703,051 11,253,288 16 122 106Olinda Alpha 1,877,620 17,862,362 10 122 112Frank Bowerman 1,991,666 20,095,157 10 122 112Sacramento Co (Kiefer) 615,702 16,076,126 26 122 96Colton Refuse DisposalSite

305,682 13,664,707 45 122 77

San Timoteo 158,405 2,154,647 14 122 108Otay Annex 1,267,641 11,164,869 9 122 113Miramar 1,289,295 28,334,172 22 122 100Sycamore 817,255 6,695,706 8 122 114Tajiguas 200,084 9,766,246 49 122 73Newby Island 592,877 17,683,738 30 122 92Kirby Canyon 246,902 3,633,204 15 122 107Guadalupe Disposal Site 166,915 8,038,063 48 122 74Santa Cruz City 51,191 3,351,872 65 122 57Buena Vista Disposal Site 131,775 4,420,935 34 122 88Woodville Disposal Site 61,368 4,822,838 79 122 43Visalia Disposal Site 108,327 8,038,063 74 122 48Yolo County Central 163,841 10,449,482 64 122 58

Average 43 82


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6. Generation and utilization of landfill gas in the US

Berenyi reported that as of 1999, there were 327 LFG-to-energy plants in the US [24].Table 6 summarizes the different uses of landfill gas. Fig. 3 shows that slightly less thanthree-fourths (71%) or 231 LFG-to-energy plants produce electricity. About one-fifth(21%) sell their gas to a direct user, approximately 4% of the plants produce pipeline—quality gas, and approximately 3% use the gas to produce synthetic fuels or for other uses.(Fig. 3).

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Table 6Utilization of landfill gas [13]

Direct heating applications | Use for industrial boilers| Space heating and cooling (e.g.greenhouses)| Industrial heating/cofiring

Electricity generation applications | Processing and use in reciprocating internal combustion (RIC)engines (stoichoimetric or lean combustion)| Processing and use in microturbines, gas, and steam turbines| Processing and use in fuel cells

Feedstock in chemicalmanufacturing processes

| Conversion to methanol (industrial or vehicular use)

| Conversion to diesel fuel (vehicular fuel)Purification to pipeline quality gas | Utilization as vehicular fuel

| Incorporation into local natural gas networkSoil remediation | Leachate evaporation system.Heat recovery from landfill flares | Using organic Rankine cycle

| Using Stirling cycle engines

Uses of LFG-to-Energy Plants in US

Electricity72%

Pipeline Quality4%

Direct Heating21%

Synfuel/Other3%

Fig. 3. Types of landfill gas utilization in the United States [24].


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Fig. 4 provides a breakdown of the US landfill gas used for energy generation in eachstate. California has the largest number of landfill gas facilities, with 65 plants, because ofstate and local requirements resulting in the collection and control gas. Other states withsignificant number of plants include Illinois (43), Michigan (22), New York (20) andPennsylvania (19).Table 7 provides some characteristics of the landfill gas projects by each state. The total

active area of landfills provided with landfill gas collection is around 21,000 ha, while alittle more than the half of this area is devoted to methane recovery (12,000 ha). The statesof California, Illinois, Michigan, New York and Pennsylvania represent approximately50% of total of devoted area to methane recovery. On the other hand, California,New York, Illinois, Texas and Michigan represent about 60% of total of refuse buried inlandfills with gas collection.The average landfill depth in the gas-collecting landfills ranges from 14–53m; the nation-

wide average depth is 28m. The density of the MSW buried in these landfills ranges from594 to 832 kg/m3, while the national average is estimated at 732 kg /m3.Table 8 provides data related with landfill gas collection by state, and also considers the

amount of municipal solid waste landfilled annually in each state (Solid Waste Digest [25]).The largest amount of MSW landfilled is landfilled in California, with around 35 milliontonnes /y. Other significant landfillers are Pennsylvania, Texas, Illinois, Michigan, andOhio.The total landfill gas collected is around 7 billion Nm3 annually, while the landfill gas

processed (i.e. excluding flaring) is 5 billion Nm3 annually and represents about 70% of thebiogas collected. The states of California, Illinois, Michigan, Pennsylvania and New Yorkrepresent 60% of total of landfill gas processed to generate energy (heat, electricity or fuel).The heating value of untreated landfill gas ranges from 464 to 591 kJ /Nm3(average:

540 kJNm!3).

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Number of LFG-to Energy Plants per State in 1999

0 10 20 30 40 50 60 70

WIVATXSCPANCNJ

MOMALAIAHI

DECAAL

Number

Fig. 4. Number of landfill gas to energy plants per state [24].


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7. Electricity generation

The US Environmental Protection Agency(USEPA), operates a Landfill MethaneOutreach Program that encourages landfill owners to develop gas recovery projectswherever it is feasible.USEPA estimates that over 700 landfills across the United Statescould install economically viable landfill gas energy recovery systems, but only 380 energyrecovery facilities were in place in 2004 [26]. Currently, 295 of these facilities generateelectricity; the rest use landfill gas for heating, reducing volume of leachate, etc.

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Table 7Characteristics of LFG projects by state [24]

State Number of LFGprojects

Active area Devoted areaCH4 recovery

Refuse buried Averagedepth

Average densityrefuse

(ha) (ha) (tonnes) (m) (kg/m3)

Alabama 2 236 16 1,306,359 14 653Arizona 5 285 254 17,418,126 29 693Arkansas 1 57 57 4,717,409 18 772California 65 5,746 3,570 546,179,234 36 730Colorado 1 36 36 27,215,821 26Connecticut 5 147 109 12,655,357 32 733Delaware 2 146 53 8,527,624 23 653Florida 12 697 530 69,971,877 25 731Georgia 4 160 68 15,694,457 24 698Hawaii 1 17 17 1,195,500 23 594Illinois 43 1,743 1,087 117,968,430 26 814Indiana 4 163 93 10,886,329 22 832Iowa 3 210 62 11,974,961 23 761Kansas 3 482 77 19,958,269 18 713Kentucky 1 304 122 n/a 46 891Louisiana 2 209 122 n/a 53Maryland 4 233 128 14,424,385 21 624Massachusetts 16 345 267 20,638,665 25 752Michigan 22 1,038 697 67,676,676 24 744Minnesota 5 190 158 20,303,003 25 743Missouri 2 100 37 12,185,430 46 594New Hampshire 6 158 151 10,646,829 28 713New Jersey 11 770 492 62,367,776 23 790New York 20 1,050 619 152,041,187 38 812North Carolina 15 723 435 31,942,937 24 695Ohio 6 383 245 47,718,407 23 792Oregon 5 531 139 14,116,847 29 812Pennsylvania 19 1,496 572 64,773,655 32 736Rhode Island 1 62 47 10,886,329 46 653South Carolina 4 84 37 5,663,612 18 653Tennessee 3 181 116 12,428,558 35 793Texas 8 865 475 117,730,352 22 730Vermont 2 24 13 1,327,225 25 653Virginia 7 347 190 29,393,087 26 754Washington 5 663 364 35,017,690 34 817Wisconsin 12 546 289 39,335,934 25 759

Total 327 20,426 11,742 1,636,288,340

The reported data corresponds to 36 states (modified from Berenyi).Note: n/a: no available.


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Through the Outreach Program, USEPA is working with municipal solid waste landfillowners and operators, states, utilities, industry and other federal agencies to lower thebarriers to economic landfill gas energy recovery.Table 9 compares the electricity generated by landfill gas to energy plants in each state

according to Berenyi [24] and USEPA [26]. The amount of landfill gas processed is around5 billion Nm3 (Table 8), and generates about 912,000 kW, equivalent to 8 billion kWh /annum (Table 9).

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Table 8Landfill gas capture by state [24,25]

State MSW landfilled(solid wastesdigest)

Landfill gascaptured(Berenyi)

Landfill gas used(Berenyi)

LFGprocessed

Heating valueuntreated gas

(tonnes/yr) (Nm3/yr) (Nm3/yr) (%) (KJ)

Alabama 5,110,224 446,559 446,559 100 580Arizona 6,460,129 8,186,916 n/a n/a 531California 35,188,243 1,952,168,440 1,408,295,409 72 500Colorado 6,269,618 3,096,143 3,096,143 100 514Connecticut 257,643 55,819,881 20,497,060 37 543Delaware 1,587,590 38,538,046 20,675,684 54 501Florida 16,248,753 245,796,024 189,780,153 77 550Georgia 10,827,361 33,581,240 33,581,240 100 563Hawaii 595,119 21,702,770 21,702,770 100 528Illinois 17,972,421 635,117,780 486,899,870 77 547Indiana 6,097,251 66,983,857 21,137,128 32 522Iowa 1,835,254 20,675,684 20,675,684 100 554Kansas 2,835,889 36,179,553 36,179,553 100 528Kentucky 4,486,075 21,434,834 n/a n/a n/aMaryland 2,849,497 53,333,829 31,005,877 58 543Massachusetts 1,406,151 203,407,647 111,848,156 55 535Michigan 16,686,020 455,795,378 417,920,820 92 559Minnesota 1,978,590 135,977,230 131,065,081 96 513Missouri 4,066,951 56,564,146 37,213,254 66 580New Hampshire 1,629,321 72,238,369 72,238,369 100 574New Jersey 3,594,303 350,548,853 223,279,524 64 534New York 6,647,011 445,472,421 336,958,573 76 543North Carolina 6,630,681 113,296,992 85,221,081 75 552Ohio 12,572,802 182,970,127 124,566,158 68 563Oregon 4,870,725 16,954,359 16,954,359 100 520Pennsylvania 22,458,496 556,625,930 363,379,983 65 545Rhode Island 1,375,306 86,334,749 86,334,749 100 570South Carolina 5,271,705 14,260,119 11,163,976 78 563Tennessee 5,877,710 79,963,840 35,665,183 45 591Texas 21,501,406 312,839,422 278,768,621 89 547Vermont 410,052 6,981,206 6,981,206 100 475Virginia 12,157,307 104,078,029 77,403,568 74 563Washington 4,692,008 253,050,127 13,099,065 5 464Wisconsin 6,263,268 199,492,812 184,160,952 92 540

Total reporting 253,814,753 6,811,497,272 4,901,214,602


!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

In the more recent survey by USEPA [24] the amount of electricity generated fromlandfill gas was estimated at 1.07GW.

8. Conclusions

On the basis of the theoretical and experimental information presented above, it can beassumed that, under the right conditions, at least 50% of the ‘‘latent’’ methane in MSWcan be generated within one year of residence time in a landfill, while the landfilled area isnot capped and rainfall can penetrate into the landfilled mass. This would correspond toabout 50Nm3 of methane /tonne of a typical MSW. However, the 25 California landfillsthat we examined in detail captured only 43Nm3 of methane per tonne landfilled. Ofcourse, conventional landfills are far from perfect bioreactors. Also, we have noinformation as to the effectiveness of the gas collection of these landfills.

Nearly three hundred eighty landfills in the US capture 3.7 billion Nm3 of methane (2.6million tonnes) of which 70% is used to generate thermal or electrical energy. The rest isflared, because it is not considered to be of economic use. There are nearly 1400 landfillsthat do not capture any biogas.

If it were possible to build and operate bioreactor landfills, where water is added andnearly all the generated methane is captured, the methane collected in the US, at anassumed average rate of 50Nm3 of methane per tonne of MSW, would amount to 11billion Nm3 of methane, i.e. three times the amount that is presently captured.

With regard to the global picture, an ongoing study [27] estimated the global dispositionof MSW in landfills to be 1.5 billion tons of MSW. The corresponding generation ofmethane is estimated to about 50 million tonnes, of which only a total of 5 million tonnes

ARTICLE IN PRESS

Table 9Electricity generation by using LFG [24,26]

State Electricity produced (kW) State Electricity produced (kW)

Berenyi 1999 USEPA 2005 Berenyi 1999 USEPA 2005

Alabama 4,000 n/a Missouri 800 n/aArizona 18,425 10,350 Nebraska n/a 3,200California 237,570 255,935 New Hampshire 15,700 13,800Colorado 800 n/a New Jersey 48,900 45,700Connecticut 9,840 5,000 New York 46,047 48,300Delaware 1,500 n/a North Carolina 10,350 11,600Florida 19,800 39,830 Ohio 8,500 36,200Georgia 5,400 7,400 Oregon 5,660 5,600Hawaii 3,000 n/a Pennsylvania 46,350 68,400Illinois 177,766 153,934 Rhode Island 12,000 17,000Indiana 7,525 21,585 South Carolina n/a 8,400Iowa 8,500 6,400 Tennessee 7,000 7,200Kansas 3,000 n/a Texas 15,600 57,656Kentucky n/a 10,400 Vermont 1,500 1,200Maryland 7,250 8,050 Virginia 14,600 31,800Massachusetts 27,650 37,744 Washington 15,700 15,200Michigan 79,900 72,300 Wisconsin 29,000 47,375Minnesota 25,800 24,200 Total 911,433 1,071,759


!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

are captured at this time. Therefore, methane emissions to the atmosphere are in the orderof 45 million tonnes. Since methane has 23 times the global warming potential of carbondioxide (CO2), global landfill emissions correspond to about one billion tonnes of CO2.

Acknowledgements

The authors gratefully acknowledge the provision of experimental data and otherassistance of Prof. Morton Barlaz of North Carolina State University, the compilation oflandfill biogas data by Dr. Eileen Berenyi of Governmental Advisory Associates, and thesupport of research at Columbia University by the Waste-to-Energy Research andTechnology Council (www.columbia.edu/cu/wtert).

References

[1] Energy Information Administration. Emissions of Greenhouse Gases in the United States 2003. Comparisonof global warming wotentials from the IPCC’s second and third assessment reports; http://www.eia.doe.gov/oiaf/1605/ggrpt/global.html

[2] Willumsen H. Experience with landfill gas recovery plants. Renewable Energy 2003; www.sovereign-publications.com/renewable-energy2003-art.htm

[3] Willumsen H. Energy recovery from landfill gas in Denmark and worldwide; www.lei.lt/Opet/pdf/Willumsen.pdf

[4] California Energy Commission. Landfill gas-to-energy potential in California; 2002; http://www.energy.ca.gov/reports/2002-09-09_500-02-041V1.pdf

[5] Themelis NJ, Kaufman SM. Waste in a land of plenty. Waste Management World; Sept–Oct 2004p. 23—8.[6] Kaufman SM, Goldstein N, Millrath K, Themelis NJ. The state of garbage in America. BioCycle 2004:31–41.[7] USEPA. Municipal solid waste generation, recycling, and disposal in the United States, Facts and Figures;

2003;www.epa.gov/epaoswer/non-hw/muncpl/pubs/msw05rpt.pdf[8] Code of Federal Regulations. Title 40:Protection of Environment, part 258-Criteria for municipal solid waste

landfills; http://www.epa.gov/epacfr40/chapt-I.info/chi-toc.htm[9] USEPA. Development document for final effluent limitations guidelines and standards for the landfills point

source category. EPA-821-R-99-109. Washington, DC; 2000; http://www.epa.gov[10] European Union. Council directive 99/31/EC; http://europa.eu.int/comm/environment/waste/landfill_

index.htm[11] Tchobanoglous G, Theisen H, Vigil S. Integrated solid waste management., Chapter 4. New York: McGraw-

Hill; 1993.[12] Themelis NJ, Kim HY. Material and energy balances in a large-scale aerobic bioconversion cell. Waste

Manage Res 2002;20:234–42.[13] Energy Information Administration. US Department of Energy. Growth of the landfill gas industry;1996;

http://www.eia.doe.gov/cneaf/solar.renewables/renewable.energy.annual/chap10.html[14] Barlaz M, Cowie S, Staley B, Hater G. Production of NMOCs and trace organics during the decomposition

of refuse and waste components under anaerobic and aerobic conditions. third intercontinental landfillresearch symposium Nov 29th–Dec 2nd; 2004.

[15] M Barlaz, North Carolina State University, private communication to P.A. Ulloa.[16] Verma S, Themelis NJ. Anaerobic digestion of organic waste in MSW. Waste management world, 2004; Jan.

–Feb, 20–4. (See also Verma S, M.S. thesis, Earth and Environmental Engineering, Columbia University,2003, www.columbia.edu/cu/wtert, Publications).

[17] Barlaz MA, Rooker AP, Kjeldsen P, Gabr MA, Borden RC. A critical evaluation of factors required toterminate the post-closure monitoring period at solid waste landfills. Environ Science & Technol2002;36(16):3457–64.

[18] USEPA. The role of recycling in integrated waste management in the US. Franklin Associates. MunicipalIndustrial Waste Division, Washington, DC, EPA/530-R-96-00; 1995.

[19] USEPA. International analyses of methane emissions; 2002; www.epa.gov/methane/intlanalyses.html

ARTICLE IN PRESSN.J. Themelis, P.A. Ulloa / Renewable Energy 32 (2007) 1243–12571256

!!!!!!!!!!!

[20] Stern DI, Kaufmann RK. Annual estimates of global anthropogenic methane emissions: 1860–1994. trendsonline: a aompendium of data on global change. carbon dioxide Information Analysis Center, Oak RidgeNational Laboratory, US Department of Energy, Oak Ridge, Tennesse, USA; 1998; http://cdiac.esd.ornl.gov/trends/meth/ch4.htm

[21] Subak S, Raskin P, Von Hippel D. National greenhouse gas accounts: current anthropogenic sources andsinks. Climate Change 1993;25:15–28.

[22] Earth Policy Institute. Economic grow falters: historical time series from David Malin Roodman. InWorldwatch Institute, vital signs; 2002 p. 58–9; http://www.earth-policy.org/Indicators/Econ/Econ_data.htm

[23] California Integrated Waste Management Board; http://www.ciwmb.ca.gov/landfills/Tonnage/2003/Landfill.htm

[24] Berenyi E. Methane recovery from landfills yearbook, 5th ed. Westport, CT: Governmental AdvisoryAssociates; 1999.

[25] Solid waste digest special report. Landfill capacity, vol. 14 2004 No. 9 http://www.wasteinfo.com[26] USEPA. Landfill Gas Outreach Program; http://www.epa.gov/lmop/proj/index.htm[27] Earth Engineering Center. Landfill gas generation, capture, and utilization. Study in progress; 2005.

ARTICLE IN PRESSN.J. Themelis, P.A. Ulloa / Renewable Energy 32 (2007) 1243–1257 1257

Hanson Landfill Services / City of Whittlesea

Comparative Greenhouse Gas Life Cycle Assessment of Wollert Landfill

Final report

—Comparative Greenhouse Gas Life Cycle Assessment of Wollert Landfill Version 3 Hyder Consulting Pty Ltd-ABN 76 104 485 289 http://aus.hybis.info/projects0/vc/awarded/aa002567/f_reports/f0009-aa002567-aar-03 wollert ghg lca report.docx

Hyder Consulting Pty Ltd

ABN 76 104 485 289

Level 16, 31 Queen Street Melbourne VIC 3000 Australia

Tel: +61 3 8623 4000

Fax: +61 3 8623 4111

www.hyderconsulting.com

Hanson Landfill Services / City of Whittlesea

Comparative Greenhouse Gas Life Cycle Assessment of Wollert Landfill

Final report

Author Joe Pickin

Modellers Kyle O’Farrell, Joe Pickin

Internal review Jessica North

External peer review Hannes Partl

Approver John Nolan

Date 1 February 2010!

Version 3 !

This report has been prepared for Hanson Landfill Services and the City of Whittlesea in accordance with the terms and

conditions of appointment for Comparative Greenhouse Gas Life Cycle Assessment of Wollert Landfill dated 22 May

2009. Hyder Consulting Pty Ltd (ABN 76 104 485 289) cannot accept any responsibility for any use of or reliance on

the contents of this report by any third party.

Front cover picture: Wollert Renewable Energy Facility

—Comparative Greenhouse Gas Life Cycle Assessment of Wollert Landfill Version 3 Hyder Consulting Pty Ltd-ABN 76 104 485 289 1 http://aus.hybis.info/projects0/vc/awarded/aa002567/f_reports/f0009-aa002567-aar-03 wollert ghg lca report.docx

Summary

Hanson Landfill Services (HLS) and the City of Whittlesea commissioned Hyder to undertake a

robust, credible and holistic assessment of the greenhouse performance of the HLS Wollert

landfill compared with four alternative waste management scenarios. The agreed method was

life cycle assessment. As the study is restricted to greenhouse gas implications, it represents

only a partial environmental assessment of the scenarios.

The wastes to be assessed were 144,000 tonnes of household garbage and 96,000 tonnes of

commercial and industrial garbage sent to Wollert landfill in 2008, and also source-separated

organic waste generated in 2008 from households that used Wollert landfill for their garbage

disposal. The organics waste comprised 33,000 tonnes of material in the base case.

The scenarios compared are outlined in Table S1. The scenarios were considered as

‘alternative worlds’ in which the 2008 waste streams enter fully-developed management

arrangements without any phase-in period. In two of the scenarios, garbage was processed

through mechanical biological treatment (MBT), which involves separation of waste into

fractions and treatment of the organic fraction by aerobic composting (in Scenario 1) or

anaerobic digestion (in Scenario 2).

Table S1 Description of the scenarios modelled

Scenario no.

& name

Waste type

Base case Scenario 1 Scenario 2 Scenario 3a Scenario 3b

Landfill Aerobic

MBT

Anaerobic

MBT

Food separation

with garbage collection

fortnightly weekly

Household organics – garden waste (all

councils) + food waste (Nillumbik only)* Enclosed composting

Enclosed composting Household organics – food waste (other

councils) **

Landfill

(Wollert)

Aerobic MBT Anaerobic

MBT Household garbage – non-food

Landfill (Wollert) Commercial and industrial garbage

Residuals from waste processing operations Landfill (Wollert)

Notes * Source-separated

** Source-separated for Scenario 3 only

As shown above, the residuals from waste processing facilities are all disposed to landfill, and

hence this activity is considered in the assessment.

The most important greenhouse gas issue associated with landfill is the generation of methane

from the anaerobic degradation of organic materials. Methane emissions were assessed using

the Intergovernmental Panel on Climate Change’s first-order decay model and the

corresponding instantaneous emissions model. The model parameters were populated using

data from Wollert landfill and values from reviewed literature. Of the methane potential of the

2008 waste deposited at the landfill, an estimated 56% derived from food waste and 22% from

paper and cardboard.


Like most large modern landfill operations, methane generated at Wollert landfill is collected and

burned to produce electricity for the grid. The recovered proportion of methane generated from

the 2008 waste deposits is estimated at 60% to 88%, based upon a range of sources including

direct measurement. The model credited carbon in the waste that is not emitted as equivalent to

carbon dioxide (CO2) removal from the atmosphere. It also provided credits for recovered

metals and electricity generated using recovered methane.

There is significant uncertainty about the net energy yield from anaerobic MBT. For this

parameter Hyder has relied on overseas data as these technologies have not been applied and

operated in Australia for sufficient time to produce a representative range of local data.

Other emission sources in the various scenarios included: transport; facility construction; energy

use and energy yields in waste processing; offsets for recovered recyclables; and organics

degradation and storage.

The results are presented in Figure S1 using mid-range estimated values and a standard 100

year assessment timeframe. This assessment method assigns a relative warming value to

methane on the basis that warming effects over the next century are equally important and

those thereafter are not important. The base case and Scenarios 2, 3a and 3b produced similar

outcomes, resulting in net savings of between 66,000 and 72,000 tonnes of carbon dioxide

equivalent (CO2-e). Aerobic MBT (Scenario 1) had lower net savings estimated at 33,000

tonnes CO2-e. The savings (avoided emissions) mostly arose from carbon storage (in the landfill

and compost) and product offsets (metals, plastics and especially electricity). The avoided

emissions outweighed the actual emissions, which were mostly associated with landfill methane

and process inputs.

The base case and Scenario 2 were shown to outperform Scenarios 1, 3a and 3b when the

values for two critical parameters (the methane recovery rate at the landfill and net energy yield

from anaerobic MBT) were fixed to the mid-point values. When the methane recovery rate was

put at the high end of its range, the base case (Wollert landfill) was the best performing scenario

(see Figure S2). At the low end of the methane recovery rate, the base case outperformed only

Scenario 1 (aerobic MBT). Similarly, over the range of potential values for net energy yield from

anaerobic MBT, Scenario 2 ranged from the best to the second worst option.

When the warming effects of methane and CO2 are assessed over different timeframes the

results change significantly (see Figure S3). When only warming over the next 20 years is

considered, the base case (Wollert landfill) performs worst and the other scenarios are relatively

equal. When warming effects over the next 500 years are included, the base case is best and

Scenarios 1 and 2 (MBTs) are worst.

While there was no clear ‘winner’ amongst the scenarios and technologies assessed, all of them

– including the current base case involving disposal at Wollert landfill – resulted in net savings

of greenhouse gases. The key elements that determined the extent of the savings from each

scenario were landfill methane emissions, carbon storage and recovery of energy.

!


The following conclusions can be drawn:

! Best practice landfill with good performance management is a potentially sound option

from a greenhouse gas management perspective.

! Anaerobic MBT appears to be a better greenhouse option than aerobic MBT. This

suggests that from a greenhouse gas perspective it is better to focus on maximising

energy recovery from biological material rather than to generate stabilised organic

products. The low-range estimate of net electricity output from Wollert landfill (around 150

kWh/t) greatly exceeded the high-range estimate for anaerobic MBT (68 kWh/t).

! Diversion of household food organics to the compost stream has a similar performance

(but usually slightly worse) to disposal at Wollert landfill, from a greenhouse gas

perspective.

! When food is diverted it makes little difference from a greenhouse perspective whether

garbage is collected weekly or fortnightly.

Figure S1 Results using mid-range parameter values assessed over a 100 year instantaneous emission basis

-150

-100

-50

0

50

100

Wollert landfill

1 - Aerobic MBT

2 -Anaerobic

MBT

3a - Food separation, fortnightly garbage

3b - Food separation,

weekly garbage

Gre

enho

use

gas

emis

sion

s (k

t CO

2-e) Methane from landfill

Emissions from other organic degradation processes

Transport

Process inputs

Product offsets (electricity, recyclables & compost)

Carbon storage

Net emissions


Figure S2 Results with high (88%), mid (74%) and low (60%) values for methane recovery from landfill, and high (68 kWh/t) and low (0 kWh/t) net electricity yield from anaerobic MBT. The charts use mid-range values for other parameters and a 100 year instantaneous emission assessment. Only Scenario 2 is affected by changes to the anaerobic MBT energy yield so the results for the other scenarios are not shown.

Figure S3 Results using different approaches in relation to time (mid-range parameter values)

-120

-100

-80

-60

-40

-20

0

High methane recovery

from landfill

Mid-range methane recovery

from landfill

Low methane recovery

from landfill

High net energy

yield from anaerobic

MBT

Low net energy

yield from anaerobic

MBT

Gre

enho

use

gas

emis

sion

s (k

t CO

2-e)

Wollert landfill

1 - Aerobic MBT

2 - Anaerobic MBT


3b - Food separation, weekly garbage

-125

-100

-75

-50

-25

0

Time sensitive, 20 years

Instantaneous emissions, 100

years

Instantaneous emissions, 500

years

Gre

enho

use

gas

em

issi

ons

(kt C

O2-

e)

Wollert landfill

1 - Aerobic MBT

2 - Anaerobic MBT


3b - Food separation, weekly garbage

High methane recovery

from landfill

Mid-range methane recovery

from landfill

Low methane recovery

from landfill

High electricity yield from anaerobic

MBT

Low electricity yield from anaerobic

MBT


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